1. Field of the Invention
The present invention relates to electronic test equipment, and more particularly to a test fixture for testing a printed circuit board assembly.
2. Related Art
Automatic test systems have generally been found to be effective for use in testing printed circuit board assemblies of various types. Such systems are particularly useful when testing large quantities of identical printed circuit board assemblies, such as computer motherboards. Most currently available automatic test systems comprise test computers having software which enables them to be used for testing various portions of printed circuit board assemblies, as well as for testing various specific electrical components which are attached on the printed circuit board assemblies. In order to electrically interconnect automatic test systems to printed circuit board assemblies, it has generally been necessary to use test fixtures that are adapted to receive specific printed circuit boards having predefined configurations.
A typical conventional test fixture includes a fixed board for positioning the printed circuit board assembly, and a movable board commonly arranged above the fixed board. The movable board is for carrying an array of test probes and/or cards to electrically interconnect automatic test systems to the printed circuit board assembly. It is important that the fixed board, which positions the printed circuit board assembly to be tested, be parallel or substantially parallel to the movable board throughout the testing procedure. If the movable board and the fixed board are not parallel to each other during testing, the test probes or test cards will not be accurately connected with the printed circuit board assembly or components attached on the printed circuit board assembly. As a result, the testing is prone to error or may even fail. Furthermore, the printed circuit board assembly and/or its attached components are liable to sustain damage.
Taiwan Patent No. 370197 discloses a motherboard test fixture comprising a fixed board and a movable board. The fixed board comprises a plurality of positioning pins engaging in positioning holes of the motherboard to be tested. The movable board carries a plurality of test cards connecting with the motherboard during testing. The movable board further comprises a plurality of spring loaded-pressing pins pressing a component side of the motherboard.
The above-described motherboard test fixture is suitable for conventional motherboards consisting of a printed circuit board and a plurality of electrical components mounted thereon. However, many recently developed motherboards have a highly complicated circuitry pattern and more electrical components mounted thereon. This requires the motherboard to be mechanically strong enough to hold the components securely. Therefore, a reinforcing plate is mounted to a solder side of the motherboard. The reinforcing plate functions only as a strengthening device shield. Therefore, the reinforcing plate is generally manufactured and installed with relatively low precision, to reduce manufacturing costs and save time.
However, this imprecision gives rise to a problem in the testing procedure. Because the reinforcing plate is not precisely mounted, it is not positioned parallel to the motherboard. As a result, it is problematic to position the motherboard parallel to the movable board of the conventional test fixture.
In spite of the above mentioned problems, the reinforcing plate is still widely used in the motherboard field. This is because many manufacturers consider that the benefits of the imprecisely made reinforcing plate outweigh the above mentioned problems. However, there remains a clear need for a test fixture that enables a motherboard having a reinforcing plate to be precisely positioned thereon.